Micromachined integrated valves are known in the prior art. Examples of various embodiments of such normally open valves are given in U.S. Pat. Nos. 4,821,997 and 4,824,073 and 4,943,032 and 4,966,646; the disclosures of which are hereby incorporated by reference herein in their entirety.
U.S. Pat. Nos. 5,865,417 and 6,149,123 taught how to make a normally closed, micro-machined valve with a leak rate on the order of 1×10−9 scc-atm/sec or less of helium. U.S. Pat. No. 6,160,243 disclosed alternative methods of actuating micro-valves. U.S. Pat. Nos. 5,865,417 and 6,149,123 and 6,160,243 are included by reference herein in their entirety.
An integrated micro-valve, also commonly referred to as a microminiature valve, uses a thin flexible membrane with an actuator to move a valve element. In some embodiments, the flexible membrane is coupled to a cantilever element through a solid extension located on the membrane, as described in the referenced patents and shown in FIGS. 1 and 2, slightly modified from as presented in U.S. Pat. No. 6,149,123. Movement of the membrane 200 causes a cantilever element 300 to move and either open or close off valve seat 410. Port 400 is fluidically coupled to passageways serving as input 520 and output 510 channels. Element 210, typically referred to as a pedestal, is joined to cantilever 300 by an appropriate adhesive or other bonding technique. In FIG. 2 the membrane 200 is actuated and the cantilever 300 is now open. Element 415 is a compliant seat material meant to facilitate sealing against valve seat 410; typically this material is a Teflon-like material, either PTFE or derivatives thereof.
As previously disclosed, membrane 200 is typically 40 to 60 microns thick and of single crystal silicon. The burst strength of the membrane is quite sensitive to design considerations such as overall area and membrane thickness. Processing conditions such as etchants and etching conditions and other variables are also factors in membrane strength. As the inlet pressure in channel 520 increases the force required to open cantilever 300 increases; in addition, as the area of channel 400 increases the opening force also increases. Depending upon the actuation mechanism employed in region 130 of FIG. 1 membrane 200 may not expand outward uniformly; the membrane may expand in such a fashion that the cantilever remains unopened or insufficiently open to meet the design criteria.
The previously disclosed valves were not able to operate reliably above an, inlet pressure of 50 psig, pounds per square inch gauge, while delivering more than 10 slm, standard liters per minute, at an acceptable pressure drop. There is a need for a valve which can flow up to 20 slm at an inlet pressure of over 100 psig with an acceptable pressure drop.